1. Field of the Invention
The present invention relates to an image forming apparatus, including a copying machine, a printer, and a facsimile apparatus, that forms a toner image made on an image bearing member such as a photosensitive member, on a recording material. In particular, the present invention relates to a transfer device that transfers the toner image to the recording material.
2. Description of the Related Art
In a transfer nip that nips a recording material and electrostatically transfers a toner image to the recording material, a pre-transfer charging unit that charges toner on a photosensitive drum before transfer is provided to adjust a charge amount of the toner.
Japanese Patent Application Laid-Open No. 2005-181906 discusses a configuration in which a pre-transfer charger increases a charge amount to suppress toner scattering.
A bulge referred to as a burr is formed at an edge of a recording material as a cutting trace that is generated when the recording material is cut to a predetermined size. If the bulge at a leading edge of the recording material enters the transfer nip, an interval between the image bearing member and a transfer member is pushed out and widened. The interval can turn back under pressure of a spring applied to the transfer member when the bulge is out of the transfer nip. As a consequence, an undesirable impact can be made.
If the bulge is formed at the leading edge of the recording material, the toner on the image bearing member just before the bulge enters the transfer nip can be scattered. It is advantageous that the charge amount of the toner image is increased before the transfer to suppress the toner scattering. However, if the charge amount is continuously large, the lifetime of the charger can be shortened because the charger easily gets dirty with the toner.